S.K.H LEUNG KWAI YEE SECONDARY SCHOOL
F.7 CHEMISTRY NOTES (AL)
CARBONYL COMPOUNDS
by
F.7B(2000/01) Hung Ka Po
Objective:
o
o
o
o
o
Describe the structure: of aldehydes and ketones, the C in C= 0 is sp2
hybridized
Recognize that benzaldehyde and phenylethanone are examples of aromatic
carbonyl compounds
State the major preparations of:
:
aldehyde by mild oxidation of 10 ROH
:
ketone by oxidation of 20 ROH
Recognize that the C in C=O is a positive centre and can be attacked by
nucleophiles
Explain the order of reactivities of aldehydes and ketones towards
nucleophilic addition reaction:in terms of electronic effect and steric effect
of alkyl group:
. HCHO > RCHO >RCR’O >CHO >CRO > CO ( REFERS TO BENZENE)
o the main reactions of aldehydes and ketones:
 nucleophilic addition of HCN
 nucleophilic addition of NaHSO3
 addition elimination (condensation) reactions with NH2OH and ,2,4-DNPH
. Oxidation (aldehyde can be easily oxidized to RCOOH, but ketone is
resistant to oxidation & cannot be easily oxidized)

Reduction to ROH by LiAIH4 and NaBH4 (aldehyde to 10 ROH, ketone to
20 ROH)
. Triiodomethane reaction for CH3COR(H) (an oxidation reaction)

Oxidation by Cu(ll) as in Fehling's reagent and Ag(l) as in Tollens' reagent

Describe the mechanism of the nucleophilic addition of HCN on carbonyl
compounds

Recognize that the reaction between sodium hydrogensulphate (IV)' and
carbonyl compounds can be used for the purification of carbonyl compounds

Recognize that the formation of 2,4~dinitrophenylhydrazone of carbonyl
compounds can be used for the identification of carbonyl compounds
Describe identification of aldehydes and ketones by

the preparation of the derivative of a carbonyl compound e.g.
2,4-DNPH
 Tollens’ reagent (Silver mirror test)
 Fehling’s solution
State the major uses of carbonyl compounds:
methanal in the manufacture of urea-methanal resin
 prepanone as a solvent and a raw material in the manufacture of the
condensation polymer perspex
Complete the equations of the following tables which gives the
important methods of preparing aldehydes and ketones. State
any special reaction conditions and name the organic reactants
and products.
General methods
ANSWERS
A)
warm with acidified dichromate, distil off
1. oxidation of alcohols
immediately to prevent further oxidation giving
a) to aldehyde
C2H5OH

CH3CHO
b) to ketone
CH3CHOHCH3

B)reflux with acidified dichromate, giving CH3COCH3
2. hydrolysis of germ dihalide
a) to aldehyde
C6H5CHCl2

b) to ketone
CH3CCl2CH3 
3. thermal decomposition of
calcium salts of carboxylic acids
a)
to aldehyde (CH3COO)2Ca

b) to ketone
(CH3COO)2Ca

4. Friedel crafts reaction to aromatic
ketones
a)  + CH3COCl

A)reflux with dilute alkaline giving C6H5CHO
b) reflux with dilute alkaline giving CH3COCH3
a)heat solids with calcium methanoate, poor yield giving
CH3CHO and CaCO3
b) heat solids, poor yield giving CH3COCH3
A)heat with AlCl3catalyst giving COCH3+ HCl
QUESTIONS in CONVERSIONS:
Reactant
1.CH3CH2OH
2.CH3CHOHCH3
3.HCCH
4.CH3COCl
5.CH2CH2
6.(CH3COO)2Ca
conditions
Finely divided Cu, 300oC
Finely divided Cu, 300oC
H2SO460oC
H2Pd-BaSO4
CO,H2, 180oC
Heat
products
CH3CHO
CH3COCH3
CH3CHO
CH3CHO
CH3COCH3, CH3CH2CHO
CH3COCH3
7.CH3COOH
8.CH3COCl
9.C6H5COCH3
MnO 300oC
(CH2)2Cd
NaOH / Br2
LQ
1.What properties of 2,4-DNPH
derivatives of carbonyl compounds
make them suitable for identification
purposes?
2.owning to careless labeling, a
confusion in laboratory store between
pentan-2-one and pentan- 3-one, each
of which boil at 102oC. describe how
you can distinguish between them?
3.arrange the following compounds in
order of increasing b.p, CH3COOH,
CH3CONH2, CH3COCH3. Explain your
answers
4. give one use of each compounds,
methanal ethanal, propanone,
benzenecarbaldehyde
CH3COCH3
CH3COCH3
C6H5COO-Na+ CHBr3
They are all crystalline solids with well
defined melting points.
Into a boiling tube, add about 10 drops of
the unknown ketones and about 5c.c of
2,4-DNPH and stir. Filter off the
crystalline ppt. And wash with little
methanol. Dissolve the crystal in minimum
of hot ethanol and cool the solution. filter
off the crystal, allow them to dry and
check their m.p.The m.p can then be
checked against a table of 2,4-DNPH
derivatives
CH3COCH3 < CH3COOH < CH3CONH2,
Of the three compound listed,
ethanamide has the highest boiling point
because it has the potential t form
multiple H-bonds between molecules, all
the bonds must be broken before the
compound can pass to vapour phase.
ethanoic acid, however, has fewer
H-bonds compared with ethanamide.
Propanone has no possibility forming
H-bonds and the molecules cling together
merely by the effects of other
dipole-dipole interactions, which are
weaker.
Methanal is used to make bakleite for
heat insulation and electrical insulator. It
is also used in the manufacture of
urea-methanal resin. Most of the ethanal
produced goes to make organic compounds
like ethanoic acid. Propanone is a very
versatile solvent and is used in one of the
method manufacturing perpex.
Benzenecarbaldehyde is used in favouring
and perform.
Observations
Carbonylcompoun NaHSO3
Tollen’s
d
reagent
HCHO
React Silver mirror
but no
ppt.
CH3CHO
React Silver mirror
but no
ppt
CHO
White Silver mirror
ppt
slow
CH3COCH3
White
No
ppt
COCH3
No
No
reaction
Fehling’s
reagent
Red ppt
iodoform
Red ppt
Yellow ppt Brown resin
No ppt
Conc.
alkaline
No resin
No
No ppt
No
No
Yellow ppt
No
No
Yellow ppt
no